The present invention relates generally to telecommunications and, more particularly, to telecommunication conductor test circuits and methods for using such telecommunication conductor test circuits.
Network Interface Devices (NIDs) are used by telecommunications companies to connect connector wires of a multi-core cable to service wires that extend to customer residences or places of business. Such NIDs are typically mounted outdoors at a customer residence or place of business. The telecommunications company multi-core cable typically extends from a switching center commonly referred to as a central office (CO) to provide communications service to one or more neighborhoods including a plurality of customers. Thus, once a pair of wires, typically referred to as tip and ring lines, from the multi-core cable are connected to a customer""s service wires, a connection is provided between the customer and the CO as will now be described.
Referring to the schematic illustration of FIG. 1, a typical telephone company (Telco) telecommunications multi-conductor cable 20 extends from the Telco central office (CO) 22 to feed pedestals in a neighborhood or neighborhoods. The Telco telecommunications conductor cable 20 may include 900 or more pairs of telecommunications conductor wires. At a splice 24, one or more of the pairs of telecommunications wires are accessed. FIG. 1 illustrates a single pair including a tip conductor 26 and ring conductor 28 which are spliced at the splice 24 into a cable extending to pedestal 32. Note that, while only one pair of wires 26, 28 is illustrated, the splice typically includes bridge connections for 25 pairs of wires with a 25 pair cable 30 extending from the splice 24 to the pedestal 32.
In the pedestal 32, the telecommunications wire pair 26, 28 is connected to a terminal block 34. It is further to be understood that, while only one terminal block 34 is illustrated, a terminal block assembly including a plurality of module stations, which may share a common base, is typically provided for all the pairs of the cable 30. The terminal block 34 provides a connection point between telecommunications wire pair 26, 28 and the customer service wires 36. A telecommunications connection may thus be provided between the customer 38 and the Telco central office 22.
As is further shown in the illustration of FIG. 1, an additional demarcation point between incoming telephone company lines and customer service wires is provided by the NID 40 which may be mounted on the premises of the customer 38. The NID 40 typically includes one or more terminal connection devices which are also typically referred to as network interface devices. The connector device in the NID 40 typically includes a removable jumper cable allowing convenient breaking of the connection between the customer service wires inside the premises of the customer 38 and the telephone company side of the telecommunications infrastructure. The removable jumper demarcation may use an RJ-type connector which may further provide a test port isolating customer wires from the telephone company wires. Such devices are illustrated, for example, in U.S. Pat. No. 4,945,559.
The telecommunications infrastructure as described with reference to FIG. 1 is generally directed to providing conventional voice services to a plurality of customers 38. The conductors 20, 26, 28, 36 are typically copper wires well suited to supporting voice communications. With the increased popularity of data based communications, which are typically digital transmissions, additional demands are being placed on the telephone infrastructure. For example, the Internet is growing increasingly popular with expanding information and services available to customers utilizing the Internet. The increase in content and opportunity for utilization of the Internet further may make it desirable to provide increasing data rates for communications over the telephone infrastructure.
While conventional modems designed for use over the telephone infrastructure are suited to the systems described with reference to FIG. 1, they are typically limited in their communication rate, for example, to 56 kilo bits per second (kbps). More recently, the digital subscriber line (DSL), very high data rate DSL (VDSL), asymmetrical DSL (ADSL) and other DSL technologies have been proposed for bringing higher band width information communications to homes and small businesses over ordinary copper telephone lines such as the cable infrastructure illustrated in FIG. 1. The DSL approach is intended to provide downstream communications connections at data rates from approximately 1.544 megabits per second (mbps) through 384 kbps. However, the data rate available for any individual customer 38 may depend upon a variety of characteristics of the Telco infrastructure including the distance between the customer 38 and the Telco central office 22.
The conductor wire pairs utilized for providing either analog and/or digital services between a customer 38 and the Telco central office 22 are typically tested to insure that they are of sufficient quality to provide the desired services. For example, one known approach for testing at a demarcation point of a customer premises, such as the NID 40, is the use of the maintenance termination unit (MTU). One known type of MTU is typically referred to as a half ringer. A half ringer places a resistor and a capacitor in series across the incoming telecommunications wire pair at the demarcation point to the customer premises. A typical half ringer will utilize a 470 kilo-ohm (kxcexa9) resistor in series with a one micro farad (xcexcF) capacitor. The presence of the MTU may be remotely detected from the telephone company""s central office. Accordingly, when a customer complaint is received, an individual customer wire pair can be tested remotely and the telephone company may be able to determine if the wiring problem is on the customer""s wires or the telephone company""s wires without the necessity of dispatching a service truck to the customer premises.
The MTU may be detected when the customer wires are disconnected at the test point, for example, by applying a voltage and detecting the current flow through the MTU circuit. An alternating current signal is utilized to detect the circuit as, under normal DC line conditions, no current flows through the MTU, thus avoiding unnecessary current flows through the MTU when it is not in use. Furthermore, as a typical customer telephone in an off hook condition appears as approximately 2 kxcexa9, the MTU, during transmission of voice signals, generally has no detectable impact on the perceived quality of the phone service. However, a half ringer has a disadvantage in that, when a customer phone is off hook, the typically 2 kxcexa9 characteristic of the phone is detected rather than the MTU. Such MTUs may further provide an undesirable degradation in the performance characteristics of the wire pair under high frequency signal transmission conditions, such as those utilized with DSL service. An example of such an MTU is described generally in U.S. Pat. No. 4,309,578.
A further approach to providing an MTU includes the use of a solid state thyristor (or triac) in line for one of the wire pair, typically the ring line. The gate of the thyristor is coupled back to the ring input, typically through a 20 volt zener diode. Thus, when a line voltage of greater than about 20 volts is presented across the wire pair, the thyristor is activated and the circuit is active for phone service. During test conditions, the test circuit may be presented with a lower voltage, such as 10 volts, across the wire pair which does not turn on the thyristor (or triac) and thereby, essentially, disconnects the customer phone. Current flow may then be monitored and if current flows at a low (e.g., 10 volt) condition, this may be understood to indicate a short or other defect in the telco (company side) lines. As with the previously described RC circuit type of MTU, a thyristor based MTU may provide for detection of whether a problem exists on the customer or Telco side of the wires without the necessity of dispatching a service truck to the customer location. Furthermore, the thyristor based MTU generally is not susceptible to whether or not the customer has a phone off hook during the test. However, for DSL type services, the thyristor""s inherent capacitance and distortion characteristics may distort the higher frequency signals typically used for data communications. Furthermore, different bias voltages may be utilized for DSL line service, for example, 20 volts as contrasted with the 48 volts typically utilized for analog voice services. An example of a thyristor based MTU is described in U.S. Pat. No. 4,700,380.
One known approach to line testing on digital service lines utilizes the intelligence of digital modem devices coupled to the digital service lines. For example, the test circuit located at the telephone company central office may share a common communication protocol with such a connected digital modem and exchange communications designed to establish a quality of service as is known in the art. Such an intelligent digital modem capability may provide inherent error checking as well as a variety of other line test capabilities. However, such a digital modem is typically not already installed at the time service is requested by existing analog voice customers to add digital service or on the activation of a new line.
In a typical transaction where a customer desires to add DSL service, the customer contacts a DSL supplier to request service. While some telephone company related entities, typically referred to as a competitive local exchange carrier (CLEC), independent local exchange carrier (ILEC) or a regional Bell operating company (RBOC), act as DSL suppliers, many DSL suppliers are independent. Such an independent DSL supplier typically is provided a portion of connection circuitry at the Telco central office or other location in the circuit downstream from the customer. The DSL supplier further may include a digital test head circuit within the DSL supplier circuitry. The DSL supplier circuitry for an independent is typically connected into the CLEC/ILEC/RBOC telecommunication circuitry through a cross connect. Under such circumstances the independent DSL supplier, responsive to the request from the customer, buys a line to the customer from the CLEC/ILEC/RBOC who controls the last leg infrastructure to the customer from the central office. As part of the transaction, the CLEC/ILEC/RBOC typically agrees to condition the sold line as part of the transaction. Such conditioning typically includes removing all the analog protectors, coils, half ringers, etc. provided on the line for purposes of analog services, which devices typically deteriorate digital communication services. The CLEC/ILEC/RBOC then assigns the appropriate wire pair to the independent DSL supplier through the cross connect. After the assignment, the independent DSL supplier tests the service line with its digital test head which test typically requires the existence of an open circuit at the customer location. If a line tests successfully, a truck may be dispatched to the customer location to hook up DSL modem hardware.
A problem for such independent DSL suppliers may occur where a detected DSL open circuit is not at the correct location (i.e., the desired customer location). Thus, potentially causing the testing to incorrectly indicate that the customer line is prepared and ready for dispatch of an installation service truck or a modem for customer installation. The customer may then initially obtain a hook up of his service either through a service truck or self-install only to discover that the service does not work. A typical problem resulting in this condition is where the CLEC/ILEC/RBOC service personnel identified that the cable from the Telco pedestal 32 to the customer 38 is not fit for digital service and pulled the line at the pedestal 32 on the expectation that a later service worker would install a suitable new line. Such a polled circuit may then cause an open circuit at the pedestal 32 resulting in an invalid test by the digital test head. Thus, it would be desirable to have an identifiable test circuit at the customer 38 which could be detected from the digital test head while still providing an open circuit for purposes of line testing by the independent DSL supplier.
In embodiments of the present invention, telecommunications conductor wire pair test circuits are provided. The test circuits include a switch electrically coupled to the wire pair. The switch has a first position in which the test circuit provides an open circuit across the wires of the wire pair and a second position in which the test circuit is detectable across the wires of the wire pair. An energy storage cell is electrically coupled across the wires of the wire pair so as to charge the energy storage cell when the switch is in the second position. The switch is powered by the energy storage cell. An energy monitor circuit is electrically coupled to the energy storage cell which detects an energy level of the energy storage cell. A switch control circuit switches the switch from the first position to the second position responsive to the energy monitor circuit.
In other embodiments of the present invention, the switch is a relay and may be a latching relay such as a bistable relay. The energy monitor circuit may be a micropower circuit powered by the energy storage cell. In various embodiments, the energy storage cell is electrically decoupled from a first one of the wires of the wire pair in the first (xe2x80x9copenxe2x80x9d or xe2x80x9csetxe2x80x9d) position so as not to charge the energy storage cell when the relay is in the first position. The switch control circuit switches the relay from the first position to the second position at a reset level and switches the relay from the second position to the first position responsive to the energy monitor circuit at a set level. In such embodiments, the set level is greater than the reset level.
In further embodiments of the present invention, the energy monitor circuit includes a first monitor circuit that controls switching of the relay from the first position to the second position and a second monitor circuit that controls switching of the relay from the second position to the first position. A second relay having a first position that deactivates the second monitor circuit when the first relay is in its first position and a second position when the first relay is in its second position may be included in the test circuit.
In other embodiments of the present invention, the switch control circuit includes a set switch circuit that switches the relay(s) from the second position to the first position and a reset switch circuit that switches the relay(s) from the first position to the second position. A current input source of the reset switch circuit is decoupled from the energy storage cell by one of the relays in the second position and coupled to the energy storage cell in the first position. The second monitor circuit may have a determined hysteresis. The set switch circuit and the reset switch circuit may include solid state switch devices.
In further embodiments of the present invention, the test circuit also includes a signal conditioning circuit coupling one of the wires to the first relay. The energy storage cell may be a capacitor having a capacitance selected to provide a determined discharge time for draining the capacitor to the reset level while powering the test circuit while the first relay is in the first position. The capacitor may further be selected to provide a determined charge time for charging the capacitor to the set level while the first relay is in the second position. The signal conditioning circuit may include a tuning resistor selected to provide the determined charge time for charging the capacitor to the set level while the first relay is in the second position. A bridge rectifier circuit may be electrically coupled between one of the wires of the wire pair and the first relay so that the test circuit is responsive to positive and negative polarity signals across the wire pair. A voltage regulator may be electrically coupled between the energy storage cell and the energy monitor circuit.
In other embodiments of the present invention, the latching relay includes an output electrically coupled to a first one of the wires of the wire pair through the energy storage cell. The first switched input is connected to a second one of the wires of the wire pair. The output is connected to the first switched input in the second position so as to charge the energy storage cell when the relay is in the first position and disconnected from the first switched input in the first position so as to provide a galvanically isolating open circuit across the wire pair.
In further embodiments of the present invention, a telecommunications conductor wire pair test circuit is provided including a relay electrically coupled to the wire pair. The relay has a first position in which the test circuit provides an open circuit across the wires of the wire pair and a second position in which the test circuit is detectable across the wires of the wire pair. An energy storage cell is electrically coupled across the wires of the wire pair so as to charge the energy storage cell when the switch is in the second position. The relay is powered by the energy storage cell. A switch control circuit switches the relay from the first position to the second position.
In yet other embodiments of the present invention, methods are provided for testing a telecommunications conductor wire pair. A switching test circuit is provided connected to the wire pair. An energy storage cell of the test circuit is charged with energy carried by the wire pair. An energy level of the energy storage cell is monitored. The connection of the test circuit to the wire pair is opened to interrupt charging of the energy cell responsive to detection of a set energy level of the energy storage cell during charging of the energy storage cell. The connection of the test circuit to the wire pair is closed using energy stored in the energy storage cell, to allow re-charging of the energy storage cell, responsive to detection of a reset energy level of the energy storage cell during discharging of the energy storage cell. The switching circuit may include a latching relay so that opening of the connection using the latching relay provides a galvanically isolating open circuit across the wire pair. In various embodiments, operations may include applying a voltage to the wire pair, detecting the test circuit while the connection of the test circuit is closed, detecting the open circuit across the wire pair while the connection of the test circuit is open and testing the telecommunications conductor wire pair while the connection of the test circuit is open. The test circuit may then be removed.